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In the Quest for Fuel Economy (4bbl)
https://slantsix.org/forum/viewtopic.php?t=56044		 Page 1 of 1
Author:  cam.man67 [ Sun Aug 24, 2014 6:08 am ]
Post subject:  In the Quest for Fuel Economy (4bbl)
Lucy, my '68 is a daily driver has been a wonderfully reliable car for me...however fuel economy hasn't. In the 3 years and roughly 30,000 miles I've had her, I've only had 2 fill-ups over 20mpg, and usually average around 16. The lowest I recorded was 10, but that was pre-valve adjustment after I had 2 cylinders that weren't firing last year. ;)

So...I would like to get those numbers a little. I mean, I'd love to see 20 consistently, but I'd be happy if even 18 was easily attainable.

Some specs on the motor: it's completely stock (113000 miles) aside from an Offy intake and 390 Holley 4bbl. It's running through a 904 into a 2.76 rear.

I realize the Holley isn't probably doing me any favors as far as fuel economy, but what if anything can I do to get that number up?
Author:  dartsport76 [ Sun Aug 24, 2014 11:54 am ]
Post subject: 
From the bit that I've read, and if you're not wanting to change the cam, a compression bump, bigger exhaust, and a distributor recurve would be your best bet. And maybe some slight head bowl work? I would think when it comes to port work that any improved efficiency would help, but others more experienced will chime in on that.

The only thing I really know, is you're gonna want a 2.25-2.5" sized exhaust, with a free flowing muffler of your choice.

I think with a stock can you're going to want to shave the head for 8.5-9.0 ish compression (gonna takes some measuring on your part to find how much to cut) and somewhere around 47-52° of total timing. Once again, hopefully others will chime in here with more details.

One last thing, do you have exhaust heat to your intake?
Author:  Reed [ Sun Aug 24, 2014 1:38 pm ]
Post subject: 
Dump the four barrel carb, switch to a two barrel Carter BBD or Holley 2280. Alternative, lock out the secondary throttle plates on the Holley and tune for maximum economy on the primaries.

Increase the exhaust size to 2 1/4 inches to the muffler and 2 inches after the muffler.

Use a free flowing muffler design.

Run synthetic oil and rear axle lube. 5W-30 weight engine oil.

Try running the valve a little loose - .012 intake and .022 exhaust.

Send some time recurving the distributor. THis has been discussed many times on this site. Use the search button.

Run a closed element air cleaner and rig up a cold air duct to get cool air from by the radiator instead of sucking down hot underhood air.

Run the heated air intake system.

Make sure there are no vacuum leaks and make sure the vacuum advance on the distirbutor is working and the vacuum choke pulloff is working.

Run skinny tires.

i am sure others will chime in with more.
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